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Home My WebLink AboutSubsoils Study for FoundationlGrtiffiifl'ffiffi*iifü**5020 County Road 154 Glenwood Springs, CO 81601 phone: (970) 945-7988 fax: (970) 945-8454 email: kaglenwood@kumarusa.com www.kumarusa.comAn Employcc ol¡ncd Compony Offise l¡cations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado Juty t9,2022 REcEfVË& Jenn Hiatt 3800 W. Yost Road Stillwater, Oklahoma 7 407 5 jnh@hiatthallenbeck. com Project No.22-7-344 Subject: Subsoil Study for Foundation Design, Proposed ADU/Garage, Lot 29, Lookout Mountain Rancheso TBD Lookout Mountain Road, Garfield County, Colorado Dear Ms. Hiatt: As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at the subject site. The study was conducted in accordance with our agreement for geotechnical engineering services to you dated May 5,2022. The data obt¿ined and our recommendations based on the proposed construction and subsurface conditions encountered are presented in this report. Proposed Construction: The proposed ADU/Garage will be two story wood frame construction with slab-on-grade floor and located on the site as shown on Figure 1. Cut depths are expected to range between about 3 to 5 feet. Foundation loadings for this t¡pe of construction are assumed to be relatively light and typical of the proposed t¡rpe of construction. If building conditions or foundation loadings are significantþ different from those described above, we should be notified to re-evaluate the recommendations presented in this report. Site Conditions: The ADU/Garage will be located below Lookout Mount¿in Road (County Road 120) and below an unnamed access easement which crosses the lowerportion of the site east to west. The lot is vacant of structures. A driveway from the access easement to the building site has been rough graded. Vegetation consists of dense scrub oak, brush, gtass and weeds. The building area is located on a south facing hillside and the ground surface slopes moderately to steeply down to the south. Scattered boulders and cobbles are visible on the ground surface below the building area. Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two exploratory pits at the building area and two exploratory pits in the septic disposal area. The approximate locations are shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils encountered in the building area, below about 2 feet oftopsoil, consist ofsandy silty clay. A gravelly sand and clay layer was encountered in Pit I at 3 to Yzfeet. Results of swell-consolidation testing perforrned on relatively undisturbed sarnples of sandy clay, presented GARËIËLD C$[!NTY EOMM U NITY DFVf; i.OPr,I I FJT -2- on Figures 4,5 and 6 indicate low compressibility under existing moisture conditions and light loading and the sample from Pit 2 at 6 feet showed a minor expansion potential when wetted. No free water was observed in the pits at the time of excavation and the soils were moist. Foundation Recommendations: Considering the subsoil conditions encountered in the exploratory pits and the nature of the proposed construction, we recoÍìmend spread footings placed on the undisturbed natural soil designed for an allowable soil bearing pressure of 1,500 psf for support of the proposed ADU/Garage. The soils tend to compress under load and there could be some post-construction foundation settlement. Footings should be a minimum width of l8 inches for continuous walls and,2 feetfor columns. Loose and disturbed soils encountered at the foundation bearing level within the excavation should be removed and the footing bearing level extended down to the undisturbed natural soils. Exterior footings should be provided with adequate cover above their bearing elevations for frost protection. Placement of footings at least 36 inches below the exterior grade is typically used in this area. Continuous foundation walls should be reinforced top and bottom to span local anomalies such as by assuming an unsupported length of at least 12feet. Foundation walls acting as retaining structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on-site soil as backfill. tr'loor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-on-grade construction. To reduce the effects of some differential movement, floor slabs should be separated from all bearing walls and columns with expansion joints which allow unrestained vertical movement. Floor slab control joints should be used to reduce damage due to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be established by the designer based on experience and the inteirded slab use. A minimum 4 inch layer of free-draining gravel should be placed beneath basement level slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with less than SOYo passing the No. 4 sieve and less than 2o/opassngthe No. 200 sieve. All ftll materials for support of floor slabs should be compacted to at least9íYo of maximum standa¡d Proctor densþ at a moisture content near optimum. Required fill can consist of the on-site soils devoid of vegetation, topsoil and oversized rock. Underdrain System: Although free water was not encountered during our exploration, it has been our experience in the area and where clay soils are present that local perched gtoundwater can develop during times of heavyprecipitation or seasonal runoff. Frozen ground during spring runoffcan create a perched condition. We recommend below-grade construction, such as retaining walls and crawlspace areas, be protected from wetting and hydrostatic pressure buildup by an underdrain system. Kumar & Associates, lnc. o Projec't llo. 22:1.U1 -3- If needed, the drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above the invert level with free-draining granular material. The drain should be placed at each level ofexcavation and at least I footbelow lowest adjacent finish grade and sloped at a minimum lo/oto a suitable gravity outlet. Free-draining granularmaterial used in the underdrain system should contain less than 2Yopasstngthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a maximum slze of 2 inches. The drain gravel backfill should be at least IYz feet deep. Surface Drainage: The following drainage precautions should be observed during construction and maintained at all times after the ADU/Garage has been completed: 1) Inundation of the foundation excavations and underelab areas should be avoided during conshuction. Drying could increase the expansion potential of the soils. 2) Exterior backfill should be adjusted to near optimum moisture and compacted to ' at least 95% of the maximum standard Proctor densþ in pavement and slab areas and to at least 90Yo of the maximum standard Proctor density in landscape areas. Free-draining wall backfill should be capped with about 2 feet of the on-site, finer graded soils to reduce surface water infiltration. 3) The ground surface surrounding the exterior of the building should be sloped to drain away from the foundation in all directions. We recommend a minimum slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of 3 inches in the first 10 feet in pavement and walkway areas. A swale may be needed uphill to direct surface runoff around the ADU/Garage. 4) Roof downspouts and drains should discharge well beyond the limits of all backfill. 5) Landscaping which requires regular heavy irrigation should be located at least 5 feet from the building. Consideration should be given to the use of xeriscape to limit potential wetting of soils below the foundation caused by inigation. Septic Field: Two profile pits were excavated on June 9,2022, at the locations shown on Figure 1. The subsoils exposed in the profile pits consisted of about two foot of topsoil overþing clayey sandy basalt gravel with cobbles andboulders to the bottom pit depths of 8 feet. No free water or evidence of seasonal perched water was observed in the pits and the soils were moist. The results of a gradation analyses perforrned on a sample of the soils (minus S-inch fraction) obtained from Profile Pit2 at3 to 4 feet are presented on Figure 7. T\e gradation analysis results are summarizedtn Table 1. Per our profile pit evaluations the USDA Classification of the soils is sandy loam, and the Soil Type is R-2 per State of Colorado Regulatton 43, Table 10-lA for the sandy loam. Based on the subsurface conditions encountered the tested area should be suitable for conventional type infiltration septic disposal system. Kumar&Assoclates, lnc. 6 Project No. 22.7.341 -4- Limitations: This study has been conducted in accordance with generally accepted geotechnical engineering principles and practices in this area at this tfune. We make no warranty either express or implied. The conclusions and recommendations submitted in this report are based upon the data obtained from the exploratory pits excavated at the locations indicated on Figure 1 and to the depths shown on Figure 2, the proposed type of construction, and our experience in the area. our services do not include determining the presence, prevention or possibility of mold or other biological contaminants (MOBC) developing in the future. If the client is concerned about MOBC, then a professional in this special field of practice should be consulted. Our findings include interpolation and extrapolation of the subsurface conditions identified at the exploratory pits and variations in the subsurface conditions may not become evident until excavation is performed. If conditions encountered during construction appear different from those described in this report, we should be notified at once so re-evaluation of the recommendations maY be made. This report has been prepared for the exclusive use by our client for design pulposes' We are not responsible for technical interpretations by others of our information. As the project evolves, we shouldprovide continued consultation and field services during construction to revièw and monitor the implementation of our recommendations' and to veri$r that the recommendations have been appropriately interpreted. Significant design changes may require additional analysis or modifications to the recommendations presented herein. We recommend on-site observation of excavations and foundation bearing strata and testing of structural fill by a representative of the geotechnical engineer If you have any questions or if we may be of funher assistance, please let us know. Respectfully Submitted, Kumar Associates, Inc. Louis Eller Reviewedby Daniel E. LEElkac attachments Exploratory Pits Figure Exploratory Pits Figure 3 - Legend and Notes Figures 4 through 6 - Swell-Consolidation Test Results Figure 7 - Gradation Test Results Table 1 - Summary of Laboratory Test Results Kumar & Associates, lnc' o Project No. 22-7-344 ACCESS EASEMENT ---a PIT 2 I...:,.- ''.'- 'ti ,a t' ' t.. ic P?1--,¡ 20 LOCATION OF SEPTIC FIELD A -,' rj - .1 a r.I _ri APPROXIMATE SCALE -FEET 22-7-344 Kumar & Associates LOCATION OF EXPORATORY PITS Fig. 1 PIT I 8L.7812' PIT 2 EL. 7850' PP-I EL. 7840' PP-2 EL. 7856' o 0 Y,lC=22.E DD=6E I +4=58 ' -2OO=21 t-I¡J l¿¡l! ITFfL L¡Jâ 5 5 ¡*l¡l UJl¿ I :EF-IL L¡JÕWC=23.5 DD=86 WC=21.0 DD=98 10 10 22-7-344 Kumar & Associates LOGS OF EXPLORATORY PITS Fi1. 2 c LEGEND ñ TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK BROWN. CLAY (CL), SANDY, StLTy, STIFF, MO|ST, REDDTSH BROWN. SAND (SC); GRAVELLY, CLAYEY, VERY STIFF, MOIST, GRAY, PIT I ONLY GRAVEL AND CLAY (GC-CL); WITH COBBLES AND SMALL BOULDERS, SANDY, SILTY, DENSE, MOIST, REDDISH BROWN. þ t HAND DRIVE SAMPLE. DISTURBED BULK SAMPLE. NOTES 1. THE EXPLORATORY PITS WERE EXCAVATED WITH A DEERE 55G MINI EXCAVATOR BACKHOE ON JUNE 9, 2022. 2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED. 3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOI.ATION BETWEEN CONTOURS ON THE SITE PLAN PROVIDED. 4. ÏHE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLYÏO THE DEGREE IMPLIED BY THE METHOD USED. 5. THE LINES BETWEEN MAÏERIALS SHOWN ON THE EXPLORATORY PIT LOGS REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL. 6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE BACKFILLED SUBSEQUENT TO SAMPLING 7 LABORATORY TEST RESULTS:wc = WATER OONTENT (%) (ASTM t 2216); DD = DRY DENSTTY (pct) (lSrV D 2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913)¡ _2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140). 22-7-344 Kumar & Associates LEGEND AND NOTES Fis. 5 SAMPLE OF: Pit 1 O 2.5' FROM: Sondy Sllty Cloy WC = 22.8 ?6, DD = 88 pcf NO MOVEMENÎ UPON WETTING I I l- - 1" lì \ \ I ¡nüMoÐü!ühD¡. tû4 lb f. tlr! ,wtdtol rtot t DrùâÞ4 æt ¡l ndl' dürc¡¿ ü¡ rrtth ffil otItm¡ !ñd f-od.ì.ì fÊ ha[ffiffituh##rdl¡¡K I I i I I 0x J.JI¡l =Ø1-2 zotr ô olnzoar-4 t0 22-7-s44 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4 SAMPLE OF: Pit 1 O 6' FROM: Sondy Sllty Cloy WC = 25.5 )4, DD = 66 pcf ADDITIONAL COMPRESSION UNDER CONSTANT PRESSURE DUE TO WETTING I I 1 I , \ \ \ () h o1 I l I I i I 0 -1 -2 -3 -1 -5 -6 N JI l¿J =v, I zo F- ê Jov,zoo 22-7-344 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5 SAMPLE OF: Pit 2 Q 6' FROM: Sondy Sllfy Gloy WC=21%,DD=98pcf EXPANSION UNDER CONSTANT PRESSURE UPON WETTING< \) L I N JJ l¡J =tî, I zIF o Jovtz.o(J 0 -1 -2 I t0 t00 22-7-344 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fis. 6 I n H t00 eo ao 70 æ s æ s 20 f0 o HYDROI¡ÊÎER ANALYSIS SIEI'E ANALYSIS TIYE READING at U5. SdNq $F¡Es i i i I IÆ -.J rt SAND GRAVEL FINE MEDIUM COARSE FINE COARSE to 20 Ito 4 50 80 70 l0 00 roo I- E Ep DIAMETER OF IN CLAY TO SILT COBBLES GRAVEL 5A X SAND 21 UQUID UITIT SAMPII OF: Sondy Gruvrl wtlh Sllt & Cloy t( PTASTICIÏY INDEX SILT AND CLAY 21 '6 FROM: PP-2 O 5' lhor l.d Ëulhr qpÞlt only lo lhclompls rhlch f.n lo'lld. lh.|.tllng Eporl lholl nol ba aprodücad'lxcrpt ln tull, r¡lhoul lh. vrllLn oFprcvol ol l(umar & Asdol6, lno.9.v. qnol!,¡L l€llng lr Þ.rfomld ln dccordonc! rnh ASII{ 0ô9f3, ASIì| D7928. ASII¡ Cl56 ond,/or ASIM Dll,l{). 22-7-344 Kumar & Associates GRADATION TESÏ RESULTS Fig. 7 tcrtfunnr & AssoDiaÞs, lnc.@Geotechnical and Materiáb EngineersandEnryôMffiTABLE ISUMMARY OF LABORATORY TEST RESULTSNo.22-7.344PROFILEPIT 22IPtl3to4662%tfttDEPTH2t.023.522.8988688ilATURALilotsluREcot¡'tEtlI{ATURALDRYDEilS]TY58rihlGRAVEL2tSAI{D$t2tPERCENTPASS|I¡G NO.200 stEvEt%tLTQUTD Lrilfrf%tPLASNCmDEXui¡co¡tFtt{EDcoftPREssrvESTRENGTHClayey Sandy Gravel withCobblesSandy Siþ ClaySandy Siþ ClaySandy Siþ ClaySOIL TYPE